How Do I Stop Water Hammer?

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How do I stop water hammer occurring? It only happens intermittently and only ever when using the mixer tap on one basin that's in an attic extension bathroom. I've tried turning down the stop cock to almost closed but it hasn't made any difference. Putting more clips on the pipe isn't possible as the knocking is occurring on a section under the floor.
 
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How do I stop water hammer occurring? It only happens intermittently and only ever when using the mixer tap on one basin that's in an attic extension bathroom. I've tried turning down the stop cock to almost closed but it hasn't made any difference. Putting more clips on the pipe isn't possible as the knocking is occurring on a section under the floor.
have you tried the opposite?... open it to the maximum
 
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It was on maximum. I closed it to almost shut based on other threads I've read.
 
Depends what type of system you have Mark. They all have differing hammer problems. A photo of your HW cylinder/tank would help, as few of us on here can see your system from where we sit.
 
No cylinder or tank. I have a Worcester Bosch Greenstar 37 Cdi Combi Boiler. The attic bathroom basin is the highest point on the water system if that's of any relevance. I can try to take a short video of the hammering pipe the next time it happens. There's a short visible run before it goes under the floor to the bathroom. If an arrestor is required then I'm unsure if it goes in before the hammering section or somewhere in the middle of it.
 
IMG_5965.JPG


Here's a photo. The hammering pipe is the one on the left. There's about 16 inches accessible after the 90 degree bend before it goes under the floor for roughly a further 5 feet before resurfacing behind the basin pedestal.
 
Maybe a bit tight but you could try replacing the elbow with a tee and mount the arrestor there to see if it fixes the hammer. Easy to reinstate the original layout if it doesn't work too well.
 
There's a bit of play on the pipes to probably allow that. PullerGas suggested the type of arrestor to use depends on the system. Any idea what type to use for a water and heating system run off a combi?
 
So the arrestor would fit directly to a push-fit tee along with the two pipes?
 
They usually need a half inch bsp connector screwed onto the base.
half inch bsp.jpg


Very likely you will find such a fitting to suit the plastic plumbing of your system.
 

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